The present invention relates generally to torsion damping assemblies comprising two coaxial parts mounted for rotation relative to each other for limited angular displacement, that is, one part having a web and another part including two annular guiding plates, one guiding plate disposed on each side of the web and cross members interconnecting the plates and parallel to the axis of the assembly and a circumferential array of resilient means interposed between the rotatable coaxial parts.
The present invention relates more particularly though not exclusively to torsion damping assemblies of the foregoing construction for friction clutch plate assemblies having so-called flexible centers, namely for motor vehicles.
In such a friction clutch plate assembly one of the coaxial parts carries a friction disc provided with friction lining on each side along its periphery, the friction disc being adapted to be clamped between members fixed for rotation with a shaft, in practice the driving shaft, while the other part is fixed to a hub which is adapted to be mounted on another shaft, in practice the driven shaft.
In practice, for manufacturing convenience, the annular guiding plates are identical and are provided with passages or apertures for securing a friction disc although, in fact, only one of the annular guiding plates need by equipped with such a friction disc.
Such a friction clutch assures a controlled transmission of torque between the friction disc, which is adapted to be clamped between two members fixed for rotation with a shaft, normally the driving shaft, and the hub, which is adapted to mounted on the other shaft, normally the driven shaft, that is, to damp audible vibrations which might develop along the kinetic chain of which the driving and driven shaft are a part.
It is furthermore known to insert between the web of the hub and the annular guiding plates friction means adapted to introduce a "hysteresis" effect in the operating characteristics of the friction clutch plate assembly; this hysteresis effect results, as is known, in a difference, for a given angular displacement of the annular guiding plates relative to the web of the hub, between the torque couple transmitted from the friction disc to the hub in a first direction of relative angular displacement, commonly known as the forward direction, and the magnitude of the torque couple transmitted during relative angular displacement in the opposite direction, commonly known as the reverse direction.
It has been established, in fact, that for certain uses such a hysteresis effect contributes to a limitation of vibrations and noise generated by rotary members associated with the kinetic chain which include the driving and driven shafts between which the friction clutch concerned is interposed.
According to the operating characteristics sought, at least part of the friction means employed may come into operation for a portion only of the relative angular displacement between the annular guiding plates and the web of the hub.
At any rate, in friction clutches of the present type, the friction means in question are usually formed as friction washers interposed axially between the web of the hub and one of the annular guiding plates, at the inner periphery thereof.
For certain uses, particularly friction clutches for heavy-duty vehicles, the hysteresis effect produced with the assistance of the friction washers may be found to be inadequate.
In order to increase the hysteresis effect, one might think of either increasing the surface of the friction washers involved or increasing their axial loading, or increase the mean radius of the friction clutch on which they are located and thereby the friction couple which they produce.
Taking into account the other component parts of a friction clutch it is difficult, in practice, owing to the limited radial space available, to increase the effective surface of the friction washers employed in such a clutch.
Likewise, increasing the loading exerted axially by the friction washers is difficult, by reason of the axial space requirements of the friction clutch; moreover, the practical effects of such increases are limited: the graph representing such an increase is rapidly damped and too great a spring load against the friction disc may, in operation, lead to friction material being torn away.
In order to increase the mean radius of the friction clutch against which the friction washers are applied, it has been proposed to arrange the friction washers proximate to the outer periphery of the annular guiding plates.
Yet such an arrangement encounters difficulties which result, notably, from the necessity of providing suitable means for retaining the friction washers radially.
A general object of the present invention is to overcome this drawback, to take advantage of the apertures or passages provided in outer periphery of the annular guiding plates, with a view to, as mentioned above, fixing the friction disc to one of them, the apertures or passages of the other remaining normally free.